DECLINE IN MARINE INVERTEBRATE SPECIES RICHNESS ACROSS THE MID-PLIOCENE WARM PERIOD IN THE VIRGINIA COASTAL PLAIN

The exceptional Neogene record of mid-Atlantic fossil invertebrates makes it possible to assess how shallow marine ecosystems have responded to repeated intervals of global climate change in the past. The Mid-Pliocene Warm Period (MPWP, 3.3-3.0 Ma), recorded in the sedimentary deposits of the Yorktown Formation, represents an interval of warming yielding surface temperatures approximately 2-3 °C warmer than today. The goal of this research is to quantify the impact of Mid-Pliocene warming on local species richness, diversity, and community structure of the marine invertebrate community from the Yorktown Formation in Virginia.

Bulk samples of fossils from before, during, and after the MPWP were compiled from museum and field collections sampled from 8 sites in the Coastal Plain of Virginia. Sites were selected to represent, when possible, similar paleoenvironments with respect to sediment grain size and estimated water depth. Sample were sieved, sorted, and identified to the species level, when possible. Presence/absence data were recorded for all taxa, and abundance was quantified for mollusks.

Both Shannon-Weiner metrics and rarefaction analyses suggest that species richness declined across the MPWP and did not immediately rebound to prior levels before the end of the Pliocene. Species composition, primarily abundance of specific bivalve and gastropod taxa, shifts significantly before, during, and after the interval. Community structure, quantified using detrended correspondence analysis, also shows longer-term changes in species composition. The results of this study provide insights into how modern marine invertebrate communities may be impacted by future warming.